Single 'grenade' wielding captain and unit charge into cover

"Are you certain about that? I was reading the rules for grenades and assaulting in cover and it seemed that once battle started the benefits of cover on initiative were lost. So in other words you have a BL with Hooks and his retinue without. The 'Lord assaults in cover, negates the bonus, and starts the battle on his I7. Since combat has begun with the Marines and they had their moment to (fluff wise) "hunker down" and save versus hits from the Broodlord, the 'Stealers would actually go next on their I6 followed by Marines on I4."

I was wondering if this was right or not, or what some of you think about it. A revelation for some units, or any attempt on Munchkin-ism?